HLA-DP antigens and post-streptococcal acute glomerulonephritis

Autoimmunity and Infection in Glomerular Disease

The ongoing glomerular damage of infections is not limited to the most widely known form of post-streptococcal glomerulonephritis, which is today less common in the Western world; other forms of glomerulonephritis are associated with several bacterial, viral and parasitic pathogens. The mechanisms responsible range from the direct damage of glomerular cells to the formation and deposition of immunocomplexes to molecular mimicry to the secretion of superantigens. Similarly, in the course of glomerular disease, infections are more frequent than in the general population due to the loss of immunoglobulins in urine and the immunosuppressive agents used to treat the autoimmune disease that decrease the activity of the immune system. Recognizing this two-way link, understanding its pathogenetic mechanism, and identifying the most appropriate therapeutic choice are essential for the personalized management of patients. In this continuously developing field, this short review summarizes the current state of the art as support for physicians, who are increasingly involved in managing patients with glomerular disease and infections.

Renal autoimmunity: The role of bacterial and viral infections, an extensive review

Autoimmunity is a process by which the loss of self-tolerance results in an immune attack against the body own tissues and organs. For autoimmunity to occur, various elements serving as triggers were described by which infections are considered one of the leading factors. In turn, renal involvement in autoimmune diseases, whether by an organ-specific attack, or as part of a systemic disease process, is well known. As bacterial and viral infections are considered to be common triggers for autoimmunity in general, we aimed to study their association with renal autoimmunity in particular. We performed an extensive search of the recent and relevant medical literature regarding renal autoimmunity syndromes such as infection-associated glomerulonephritis and vasculitis, associated with bacterial and viral infections. By utilizing PubMed and Google Scholar search engines, over 200 articles and case reports were reviewed. Among other mechanisms, direct infection of the renal parenchyma, molecular mimicry, induction of B-cells or secretion of superantigens, bacterial and viral pathogens were found to correlate with the development of renal autoimmunity. Nevertheless, this was not true for all pathogens, as some mimic autoimmune diseases and others show a surprisingly protective effect. The exact immunopathogenesis is yet to be determined, however. For conclusion, bacterial and viral infections are linked to renal autoimmunity by both direct damage and as mediators of systemic diseases. Further research particularly on the immunopathogenetic mechanisms of renal autoimmunity associated with infections is required.

Acute post-streptococcal glomerulonephritis: analysis of the pathogenesis

Increasing evidence supports a central role of the immune system in acute post streptococcal glomerulonephritis (APSGN), but the current view of how streptococcal biology affects immunity, and vice versa, remains to be clarified. Renal glomerular immune complex deposition is critical in the initiation of APSGN; however, mechanisms previous to immune complex formation could modulate the initiation and the progression of the disease. Initial and late renal events involved in the nephritis can also be related to host factors and streptococcal factors. In this review we describe the mechanisms reported for the APSGN pathogenesis, the interactions of streptococcal products with renal cells and leukocytes, the possible effects of different nephritogenic antigens in the renal environment and the possibility that APSGN is not just due to a single streptococcal antigen and its antibody; instead, kidney damage may be the result of different factors acting at the same time related to both streptococcus and host factors. Addressing these points should help us to better understand APSGN physiopathology.

First report on HLA-DPA1 gene allelic distribution in the general Lebanese population

Aims

HLA-DPA1 is an important marker in bone marrow and organ transplantation and a highly emerging screening parameter in histocompatibility laboratories. Being highly polymorphic, it has another significant value in detecting population origins and migrations. This is the first study to assess DPA1 allele frequencies in an Arab population.

Methods

The HLA DPA1 alleles were identified using the One-Lambda assays on a Luminex reverse SSO DNA typing system. Our study included 101 individuals coming from different Lebanese geographical areas representing the different communities and religious sects of the country.

Results

We compared the results of this study to 16 different populations and found very interesting similarities and differences between Lebanese people and individuals of European ancestry.

Conclusion

This study is the first to describe the different allelic frequencies of HLA-DPA1 in the Lebanese population and will serve as a template that can be later used for disease association studies both at the level of the country and internationally.

New trends of an old disease: the acute post infectious glomerulonephritis at the beginning of the new millenium

The association between acute renal disease and infection has been known since the mid '800s: acute post-infectious glomerulonephritis (PIGN) is a reactive immunological process against the kidney secondary to an infection, classically caused by a Streptococcus. The typical clinical presentation of PIGN is an acute nephritic syndrome with macro- or microscopic hematuria, proteinuria, hypertension, edema and renal function impairment of variable degree. The histology is characterized by an intracapillary glomerular proliferation, but may rarely be associated with an extracapillary proliferation. The classical childhood form is still present nowadays, even with severe cases, in developing countries, while in the last decades it almost disappeared in industrialized countries, where post-infectious GN are often found in elderly patients with multiple comorbidities. These clinical variants are usually related to other infective agents, like Staphylococcus aureus, both methicillin resistant (MRSA) and susceptible, and may be characterized by an IgA-dominant deposition. Kidney biopsy is rarely needed, especially in the child, while in the adult or old patient a biopsy is warranted if there is an atypical presentation or evolution, like rapidly progressive renal failure, absent or delayed function recovery, persisting low C3, nephrotic range proteinuria and persisting high proteinuria. Current therapy strategies rely on culture-guided systemic antibiotics, especially in the old patient, in which MRSA are relatively frequent, support therapy and only in very selected cases on steroids. These latter cases include the rare PIGN with crescents and those with a severe interstitial inflammation.

Bacterial infection-related glomerulonephritis in adults

In the past, most cases of bacterial infection-related glomerulonephritis (IRGN) occurred in children following streptococcal upper respiratory tract or skin infections and were called postinfectious GN. Over the past 3 decades, there has been an important shift in epidemiology, bacteriology, and outcome of IRGN. A significant percentage of cases now target adults, particularly the elderly or immunocompromised. Because adult infections are often ongoing at the time of diagnosis, the term IRGN appears more appropriate. The sites of infection in adult IRGN are more heterogeneous than in children, and include the upper respiratory tract, skin, lung, heart, urinary tract, teeth/oral mucosa, and bone. In adults, the disease is more likely to be secondary to non-streptococcal infections, particularly staphylococcal infection. In contrast to the favorable course in children, a significant proportion of adults with IRGN, especially the elderly and diabetics, do not recover renal function. Whereas the pathogenesis of post-streptococcal glomerulonephritis has been studied extensively, leading to the identification of two candidate nephritogenic streptococcal antigens, glyceraldehyde-3-phosphate dehydrogenase and pyrogenic exotoxin B, few investigations have focused on IRGN caused by other bacteria. This review will address the current status of sporadic bacterial IRGN in adults.

HLA-DRB1* alleles in Egyptian children with post-streptococcal acute glomerulonephritis

To investigate the association between HLA-DRB1* alleles and post-streptococcal acute glomerulonephritis (PSAGN) in Egyptian children, 32 unrelated patients with PSAGN and 380 healthy individuals from the same locality were typed for DRB1* alleles using the polymerase chain-reverse hybridization technique. Patients with PSAGN had significantly increased frequency of both DRB1* 03011 (46.9 vs. 19.2% in controls, P=0.00025) and DRB1* 1105 (31.1 vs. 15.6% in controls, P=0.0097) alleles. However, after correction of P values, only the difference for DRB1* 03011 allele remained significant (Pc=0.025). Their relative risks were significantly high (3.71, confidence interval [CI]=1.8-7.8, and 3.57, CI=1.4-8.9 respectively). No significant differences in the frequency of the two alleles were observed among patients with different grades of hypertension or proteinuria. In conclusion, DRB1* 03011, and possibly 1105, alleles confer susceptibility to PSAGN. However, the severity of the disease is not determined by these two alleles.

HLA-DP epitope typing using monoclonal antibodies

We have made a panel of murine anti-DP monoclonal antibodies for serological typing of HLA-DP polymorphisms; they can be used in microcytotoxicity (for 7 epitopes) and binding assays (for 8 epitopes). The antibodies detect polymorphic differences in both alpha and beta chains. As immunogens we sometimes used B-lymphoblastoid lines or purified DP molecules but mostly used mouse fibroblast transfectants expressing DP molecules. The DP beta genes were made from a cloned DPB1*0201 gene by replacing its major area of polymorphism with matching stretches of DNA amplified from other alleles; cloned DPA1*01 and DPA1*02 genes were used for transfection along with the beta chain genes. The monoclonal antibodies showed reaction patterns that correlated with the presence of particular amino-acid sequence motifs; thus none of the antibodies is allele-specific. They bind instead to epitopes which are found on a number of different HLA-DP types. We have constructed frequency tables so that the epitope (motif) data can be interpreted as the most likely genotype in each case. The basic assumption to justify this work is that HLA-DP matching or mismatching will likely influence transplant outcome, particularly in bone marrow transplantation. The present challenge is to define permissive and nonpermissive combinations of HLA-DP; it may be that matching for epitopes, rather than for full alleles, will help to resolve this issue.